Tuesday 7 October 2008 13.07 EDT
First published on Tuesday 7 October 2008 13.07 EDT

Swarms of fish have been revealed thriving in one of the most inhospitable environments on the planet – the bottom of an ocean trench.

Scientists filming almost five miles (7,700m) below the Pacific Ocean discovered groups of highly sociable snailfish swarming over the bait they laid. It is the first time cameras have been sent to this depth.

"We thought the deepest fishes would be motionless, solitary, fragile individuals eking out an existence in a food-sparse environment," says Professor Monty Priede, director of the University of Aberdeen's Oceanlab, which is leading the expedition with the University of Tokyo.

"But these fish aren't loners. The images show groups that are sociable and active. All we've seen before of life at this depth have been shrivelled specimens in museums. Having seen them moving so fast, snailfish seems a complete misnomer," he added.

Some species of snailfish live in shallow water, but the hadal snailfish are found exclusively below 6000 metres. Here they live in total darkness, near freezing temperatures and immense water pressure – 8,000 tonnes per square metre. They feed on tiny shrimp-like creatures that scavenge the carcasses of the dead fish and detritus that float down to the ocean floor.

The deep-sea equipment needed to survive the extreme pressure at these depths was designed and built by the Oceanlab team specifically for this mission. The submersible camera platforms take five hours to reach the depths of the trenches and remain on the seafloor for two days.